1. Field of the Invention
The present invention relates to a reactor for producing a carbon ring nitrile compound or a heterocyclic nitrile compound by ammoxidation of a carbon ring compound or a heterocyclic compound having organic substituents with ammonia and a gas containing oxygen in accordance with the gas phase reaction using a fluidized catalyst bed.
2. Description of the Related Arts
Carbon ring nitrile compounds are useful as raw materials for synthetic resins and agricultural chemicals and as intermediate compounds for amines and isocyanates. Heterocyclic nitrile compounds are useful as intermediate compounds for drugs, additives for feedstuffs and additives for foods.
The process of reacting an organic compound such as carbon ring compounds and heterocyclic compounds having organic substituents with ammonia and a gas containing oxygen is called ammoxidation and, in general, nitrile compounds are produced by a gas phase reaction using a fluidized catalyst.
It is known that catalysts containing vanadium, molybdenum or iron are used for the ammoxidation. For example, in Japanese Patent Application Laid-Open No. Heisei 11(1999)-209332, a process for ammoxidizing aromatic compounds and heterocyclic compounds having alkyl groups as substituents in the presence of a catalyst containing oxides of V, Cr, B and Mo is described. In Japanese Patent Application Laid-Open No. Heisei 9(1997)-71561, a process for producing dicyanobenzene by ammoxidation of xylene in the presence of a catalyst containing oxides of Fe, Sb and V is described.
As for the reactor of the gas phase reaction using a fluidized catalyst bed for ammoxidation, it is described in Japanese Patent Application Laid-Open No. Heisei 10(1998)-152463 that, in ammoxidation of methanol, a gas containing oxygen is introduced at a bottom portion of a vertical reactor, ammonia and a carbon ring compound is introduced at a side portion and the ranges of the density of the fluidized bed and the flow rates of the gases and the position of supply of the raw material are defined so that the contact between the gas of the raw material and the particles of the catalyst is improved.
It is described in Japanese Patent Application Laid-Open No. Heisei 10(1998)-120641 that, in a process for producing an aromatic nitrile by the gas phase ammoxidation, the position of the inlet of the raw material is decided in a manner such that, in the reaction zone, the ratio Wb/Wa of the amount by weight of the catalyst fluidized at the portion above the inlet for supplying the carbon ring compound (Wb) to the amount by weight of the catalyst fluidized at the portion above the inlet for supplying the gas containing oxygen (Wa) is in the range of 0.01 to 0.95. It is described that the yield and the selectivity of the aromatic nitrile of the object compound decrease when Wb/Wa exceeds 0.95.
In general, it is considered that the distribution of the temperature in the fluidized bed is kept approximately uniform when the fluidized condition within the bed is excellent. However, the distribution of the temperature is frequently not uniform when the reaction is a rapid exothermic reaction such as ammoxidation and a cooling tube is disposed for removal of heat. In particular, when the amount of heat generation per the unit volume of the fluidized bed (the density of heat generation) is great and the heat capacity of the catalyst particles is relatively small in comparison with the heat capacity of the gas phase, the distribution of the temperature is markedly uneven in an apparatus of the industrial scale having a fluidized bed and a column having a diameter exceeding 2 m. When the distribution of the temperature is uneven, drawbacks such as a decrease in the conversion and formation of byproducts arise at portions where the temperature is not optimum.
Moreover, with a reactor of the industrial scale having a fluidized bed and a column having a diameter exceeding 2 m. it is difficult that the uniform distribution of the temperature is achieved especially at the start of the operation, so it takes a long time to stabilize the temperature. As another problem, it is mentioned that the heat transfer efficiency of cooling tubes disposed in the reactor decreases when it operates for a long period time. Because of the problems mentioned above, it is difficult to achieve a stable and a long time operation.